DBCC CHECKDB('MSDB') returns errors

DBCC CHECKDB('MSDB') returns errors the following is the error Msg 8906, Level 16, State 1, Line 1 Page (1:2333) in database ID 4 is allocated in the SGAM (1:3) and PFS (1:1), but was not allocated in any IAM. PFS flags 'MIXED_EXT ALLOCATED 0_P